1.Field of the Invention
The present invention relates to a data communications apparatus which performs data communications through the telephone line and that is connected to an external information processor such as a personal computer for the external information processor to perform communications through the data communications apparatus, and more specifically, to a facsimile apparatus provided with a facsimile modem function.
2.Description of the Prior Art
A function to directly facsimile-transmit an original such as a document and a drawing made on a personal computer and to receive image data facsimile-transmitted over the telephone line to directly input them to the personal computer is called a PC-FAX function. The PC-FAX function is realized by connecting a personal computer to a facsimile apparatus having a data communications port such as an RS-232C port to use the facsimile apparatus as a facsimile modem.
In connecting a personal computer to a facsimile apparatus, an expansion board provided with an internal register is connected to, for example, an RS-232C port of the facsimile apparatus. The personal computer is connected to the facsimile apparatus through the expansion board, and the expanded function is allotted to a key of an operation unit of the facsimile apparatus.
By attaching the expansion board, various expanded functions are performed such as a function for the personal computer to transmit data via the facsimile apparatus, a function for the personal computer to receive data via the facsimile apparatus, a printer function to use the facsimile apparatus as a printer of the personal computer, and a scanner function to use the facsimile apparatus as a scanner for inputting images to the personal computer. Thus, a recording unit and an original reading unit of the facsimile apparatus can be used also as a printer and a scanner which are necessarily prepared on the side of the personal computer originally, so that it is unnecessary to prepare the expensive peripheral devices, which is very advantageous.
A facsimile apparatus connected to a personal computer operates in two modes: a normal mode (facsimile mode) in which the facsimile apparatus operates alone without performing any data communications with the personal computer; and a PC-FAX mode (facsimile modem mode) in which the facsimile apparatus performs data communications with the personal computer. The changeover between these two modes is made through control from the personal computer by using control commands called AT commands. The facsimile apparatus is usually in the normal mode. The mode is changed to the PC-FAX mode when data of the personal computer is transmitted through the facsimile apparatus or when data received by the facsimile apparatus is transmitted to the personal computer.
When the facsimile apparatus receives an AT command from the personal computer in a standby state where the facsimile apparatus performs no operation, no problem is caused if the mode is immediately changed to the PC-FAX mode. However, when the facsimile apparatus receives an AT command while operating in the normal mode, data is lost if the mode is immediately changed to the PC-FAX mode. For this reason, in a conventional apparatus, when an AT command is received from the personal computer while the facsimile apparatus is operating in the normal mode, the user decides whether the AT command is ignored or the mode is changed to the PC-FAX mode, and operates an operation unit of the facsimile apparatus according to predetermined procedures. Moreover, when the facsimile apparatus is operated in the PC-FAX mode and the operation mode is returned to the normal operation mode after the operation in the PC-FAX mode is finished, it is necessary for the user to take the necessary operation procedures.
However, it is inconvenient for the user to perform a mode setting operation every time the mode is changed and erroneous setting is readily made by mis-operation. This reduces communications efficiency.
There are various types of applications software for performing the PC-FAX function according to the types of the personal computers, and how the applications software operates differs according to the types of the personal computers. The applications software transmits ATHO (on-hook command) which is one of the AT commands to the facsimile apparatus to close the telephone line when the PC-FAX mode is finished. The ATHO command is also transmitted to close the telephone line when the user performs an interrupt operation.
However, some types of applications software interrupt the operation without transmitting any ATHO command when the interrupt operation is performed. In such a case, the telephone line is left opened. For example, if a command "call the other end of the line" is transmitted from the personal computer to the facsimile apparatus and the user interrupts the execution of the command while the facsimile apparatus is executing the command, the facsimile apparatus is in an off-hook state where the telephone line is left opened.
In such an interrupted state, since the telephone line is opened, no call can be placed via the outside line and the operation of the facsimile apparatus in the normal mode is impossible. Further, since no command is transmitted to the facsimile apparatus, even if the PC-FAX mode is canceled, the hook state cannot be returned to the on-hook state, which is very disadvantageous.
In such a situation, the hook state may be returned from the off-hook state to the on-hook state by turning off the facsimile apparatus. However, the data stored in the random access memory (RAM) of the facsimile apparatus is lost if the facsimile apparatus is turned off.